The irradiation of target metals or semiconductor materials by an ion beam provides a process for effecting the doping of such materials in a controlled and rapid manner. One method of accomplishing this process, known as ion implantation, involves electrostatically scanning (deflecting) an ion beam of controlled intensity in a selected two dimensional pattern across the surface of a target. Uniformity of the resulting doping concentration in the target is typically a primary objective of the scanning system.
In order to achieve uniform doping, it is generally desirable to electrostatically deflect (scan) the beam so that the position of the intersection of the ion beam with the planar surface of a target changes linearly with time, i.e., so that the speed of the point of intersection on the target surface is constant. The appropriate scan signal to achieve the desired uniform doping is typically generated by modifying (compensating) a triangle wave form.
One prior art compensation method and apparatus is described in Turner, U.S. Pat. No. 4,283,631 and assigned to the assignee of the present invention Another, compensation technique is described in McGuire, U.S. Pat. No. 4,593,200, which will be more fully discussed below.